Strip transmission line interboard connection



Feb. 7, 1967 w. M. FULP 3,303,439

STRIP TRANSMISSION LINE INTERBOARD CONNECTION Filed June 14, 1965 3 Sheets-Sheet 1 FIG.

/A/l/ENTO/? W M. FULP V 8 M W- M A 7 TORNE V Feb. 7, 1967 v w, PULP 3,303,439

STRIP TRANSMISSION LINE INTERBOARD CONNECTION Filed June 14, 1965 a Sheets-Sheet a FIG. 3

W. M. FULP Feb. 7, 1967 3,303,439

STRIP TRANSMISSION LINE INTERBOARD CONNECTION Filed June 14, 1965 3 Sheets-Sheet 3 FIG. 4

FREQUENCY (ac/55c.)

3E 39 EQQEQ United States Patent 3,303,439 ST TRANSMISSION LINE INTERBOARD CONNECTION William M. Fuip, Winston-Salem, N.C., assignor to Westem Electric Company, Incorporated, New York, N.Y.,

a corporation of New York Filed .iune 14, 1965, Ser. No. 463,516 12 Claims. (Cl. 333-84) This invention relates to strip transmission lines and more particularly to a connector for connecting the center conductors of two strip transmission lines stacked one upon the other.

The center conductors of stacked strip transmission lines have been connected by means of a coaxial connector arranged perpendicular to the plane of the transmission lines. These coaxial connectors usually include a metallic bellows for providing an elastic contact between the center conductor of the coaxial connector and the center conductor of the strip transmission line. Various clamping means have been employed for maintaining mechanical rigidity, all of which tend to complicate the device when used under extreme environmental conditions. Another problem is the maintenance of a good impedance match by reducing so far as possible the discontinuity existing at the connector. It is well known that discontinuities tend to be inherent at the interface between two different types of transmission lines such as the transition between a strip transmission line and a coaxial line. Various devices have been employed in the past to reduce the effects of these discontinuities. It is highly desirable, particularly where the transmission lines are to be used under extreme environmental accelerations, to maintain the integrity of the connection and thus its reliability. Due to the expense of such connectors, it is desirable that they be made as simply as possible. Moreover, the construction should not only reduce the cost but should also improve both the electrical and mechanical reliability and performance of the connection.

The objects of this invention are to simplify the connector structure for stacked strip transmission lines, to increase their reliability, reduce their cost and improve both their electrical and mechanical performance.

The foregoing objects are achieved by this invention which comprises two stacked strip transmission lines having their center conductors connected by a thin foil strip. The ground plane may also be carried along with the strip so as to maintain a substantially continuous trip transmission line configuration. Impedance matching is ac complished by adjusting the width of the foil strip. The

strip may be welded or otherwise secured to the center conductors to improve reliability under extreme environmental conditions.

The invention may be better understood by reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the connection between a pair of strip transmission lines with a portion of the upper line cut away to expose a fragmentary view of the connector assembly;

FIG. 2 is a section taken on line 22 of FIG. 1;

FIG. 3 is a fragmentary, isometric view of the structure of FIG. 1 with the connector removed;

FIG. 4 discloses another embodiment of the invention in which the center conductor of one strip transmission line continues in the same direction as the parallel center conductor of the other transmission line instead of reversing direction as shown in FIG. 2; and

FIG. 5 illustrates a typical return loss characteristic of the connector of this invention.

Referring to FIGS. 1, 2 and 3, two strip transmission lines 1 and 2 are shown stacked one upon the other. Each of these transmission lines comprises a pair of external ground planes, two dielectric layers or circuit boards, and a center conductor. Transmission line 1, for example, comprises outer ground planes formed by conductive plates 11 and 15, dielectric boards 12 and 14 and a center conductor 13. Center conductor 13 is preferably formed on the surface of dielectric board 14 by a conventional printed circuit technique. This center conductor is in the form of a narrow ribbon as illustrated in FIGS. 1 and 3. In accordance with conventional practice, the thickness of this strip is approximately 3 mils and the ground plates 11 and 15, also called ground planes, may be of the same or greater thickness. The dielectric boards 12 and 14 may be of any suitable material but for the purposes of this invention it is preferred that they be made of polyethylene or other dielectric material having similar properties.

Transmission line 2 is of similar construction having ground planes 21 and 25, dielectric boards 22 and 24 and a center conductor 23 formed on dielectric board 24. In the stacked arrangement shown in these figures, it is desired that the two center conductors 13 and 23 be electrically connected together with the least possible discontinuity through the connection.

To effect this connection, an interboard connector assembly extends through an aperture 60 in dielectric boards 14 and 24 and ground planes 15 and 25 of the two boards. The cross section of aperture 60 is rectangular as indicated in FIGS. 1 and 3. The connector 50 comprises a strip of foil 52 carried between a pair of dielectric blocks 54 and 55, the ends 51 and 53 of the foil strip being bent over to engage the ends of the inner con ductors 13 and 23, respectively. To carry the ground plane more completely through the connection, a ground plane plate 56 is also included in the aperture and makes electrical connection with ground plane portions 15A and 25A of ground planes 15 and 25, respectively.

Prior to assembly, boards 14 and 24 have center conductors 13 and 23, respectively, formed on one of their sides and ground planes ,15 and 25 on their other sides. Boards 12 and 22 have ground planes 11 and 21, respectively, formed on one of their sides. The rectangular hole 60 is punched through boards 14 and 24 as well as their ground planes 15 and 25, the center conductors 13 and 23 continuing up to an edge of this hole. Boards 14 and 24 are then put together with the rectangular holes 63 in register. The foil strip 52 is then inserted in the hole with dielectric block 54 between the strip 52 and the ends of the center conductors 13 and 23. The ends 51 and 53 are then bent at right angles so as to make contact with the center conductors 13 and 23, respectively. These may then be welded by conventional resistance welding procedures. Dielectric block 55 and ground plane 56 are then inserted after which the outer boards 12 and 22 are placed over the assembly in the position shown in these figures so that the rivet holes 36 are in register. The rivets 32 are then inserted through 3 the holes and headed as indicated at 31. The row of rivets in the rivet holes 30 are preferably spaced less than one quarter wavelength in accordance with conventional practice.

Foil strip 52 may also be about 3 mils thick and it should be emphasized that the thickness dimensions in all of the drawings are not to scale but have been exaggerated for the sake of clarity. The width of strip 52 may be adjusted so that the characteristic impedance through the connector substantially matches that of the strip transmission line.

In FIG. 3 dielectric board 12 and its ground plane 11 have been cut away to reveal the aperture 60. The upper surface of dielectric board 22 may be seen at the bottom of this aperture. To avoid a short circuit between the sides of foil strip 52 and ground planes 15 and 25, these ground planes are cut away as shown at 27 to not only provide this clearance but also to help maintain a proper impedance match. By reason of the resilience of dielectric boards 14 and 24, their inner edges will tend to come together as indicated at 26 when the rivets are installed.

The arrangement shown in FIG. 4 discloses an embodiment of the invention wherein the center conductor continues in the same direction rather than turning back as was illustrated in FIG. 2. The construction otherwise, insofar as transmission lines 1 and 2 are concerned, is identical to that shown in FIG. 2. However, in order to effect assembly, the foil strip 52 will have its lower end 53 bent to the right to engage the center conductor 23 which now extends to the right instead of to the left as was shown in FIG. 2. Instead of using rivets to hold the assembly together, screws 43 extend through holes in the transmission lines and have their ends threaded into a metal support plate 40 electrically connected to the ground planes 15 and 25. Since no center conductor exists to the right of the connector in transmission line 1, the two dielectric boards 12 and 14 form a contiguous interface at line 41. Similarly, since no center conductor exists to the left of the connector in transmission line 2, dielectric boards 22 and 24 come together at line 42. The thickness of support plate 40 should be sufiicient to receive at least three or four threads of screws 43 and also to serve the additional function of providing some additional ground plane opposite strip 52 through the connector. It must be remembered, however, that both ground planes 15 and 25, as well as support plate 40, must be cut away at the connector in the same manner illustrated by cutaway portion 27 in FIG. 3. The remaining reference numerals in this figure are identical to those shown in FIGS. 1 and 2 and relate to structures having corresponding functions in both embodiments.

The return loss characteristic shown in FIG. is typical of the characteristics obtained by the connectors of this invention. This characteristic should be considered illustrative only and'not restrictive of either frequency range or bandwidth as these are changed by altering the dimensions of the strip transmission lines as well as those of the connector; It will be evident from the foregoing description that this invention is of a'very simple construction maintaining rather closely the strip transmission line configuration throughout the region of the connector. It will also be evident that all parts are held rigidly together resulting in a very reliable construction both mechanically and electrically.

While it has been mentioned that the foil connector strip may be resistance welded to the center conductors, soldering may also be employed and, in instances where the connection is not intended to be permanent, a fairly reliable joint may be maintained merely by the pressure exerted by the dielectric boards. The invention is also not limited to having the connector foil pass through an aperture in the boards as it is obvious that it may extend between the ends of the center conductor strips at the edges of the boards providing dielectric blocks corresponding to blocks 54 and 55, or their equivalents, are carried with the foil in the same relative positions shown in FIG. 2 and a suitable ground plane, corresponding to ground plane element 56 is mounted over them and secured to ground planes 11 and 21. The resulting structure would be substantially as illustrated in FIG. 2 except that ground plane portions 15A and 25A and the adjacent portions of dielectric boards 12 and 22 would not exist and ground plane 56 would be extended up and joined to ground planes 11 and 21.

What is claimed is:

1. Means connecting strip transmission lines comprising two stacked circuit boards each containing a flat conductive strip included between a pair of conductive ground plates and separated from said plates by solid dielectric material, each of said strips having an end positioned directly opposite the corresponding end of the other strip, a conductive strip of foil having thickness and width dimensions approximating the corresponding dimensions of the fiat conductive strips in said boards, means electrically and mechanically securing said foil to the ends of said strips, and dielectric material interposed between said foil and the ground plates of said stacked circuit boards.

2. The combination of claim 1 and an electrical conductor having a surface disposed substantially parallel to a surface of that portion of said foil which extends between said strips, means connecting said conductor to said ground plates, and additional dielectric material included between said electrical conductor and said foil.

3. The combination of claim 1 wherein the width of said foil is such as to establish a substantially uniform characteristic impedance through the connecting means.

4. The combination of claim 1 wherein the width of said foil is less than that of the two strips to which it is connected.

5. The combination of claim 2 wherein the width of said foil is such as to establish a substantially uniform characteristic impedance through the connecting means.

6. The combination of claim 2 wherein the width of said foil is less than that of the two strips to which it is connected.

7. Means connecting strip transmission lines comprising a pair of stacked circuit boards each containing a fiat conductive strip included between two conductive ground plates and separated from said plates by dielectric material, each of said strips having an end so positioned that the edge of said end is substantially parallel to the corresponding edge of the end of the other strip, a conductive strip of foil having thickness and width dimensions approximating the corresponding dimensions of the flat conductive strips in said boards, means electrically and mechanically securing said foil to the ends of said strips, and dielectric material interposed between said foil and the ground plates of said stacked circuit boards.

8. The combination of claim 7 wherein the width of said foil is such as to establish a substantially uniform characteristic impedance through the connecting means.

9. .The combination of claim 7 wherein the width of said foil is less than that of the tWo strips to which it is connected. 7

10. Means connecting strip transmission lines comprising a pair of stacked circuit boards each containing a fiat conductive strip included between two conductive ground plates and separate-d from said plates by dielectric material, each of said strips having an end so positioned that the edge of said end is substantially parallel to the corresponding edge of the end of the other strip, an aperture through said boards extending between their strips, a conductive strip of foil having thickness and width dimensions approximating the corresponding dimensions of the fiat conductive strips in said boards, said foil strip'extending, through said aperture and of sufiicient length to overlap the ends of said flat conductive strips, means electrically and mechanically securing said foil to the ends of said flat strips, and dielectric material in said aperture inter;-

5 6 posed between said 'foil and the ground plates of said OTHER REFERENCES stacked clrcult boards- Bland, G. F., et al.: Coax to Stripline Transistor,"

T combination of claim 10 the Wiqth 9 IBM Technical Disclosure Bulletin, vol. 3, No. 4, Septemsaid foil 1s such as to establish a substantially uniform ber 1960, 2243 characteristic impedance through the connecting means.

12. The combination of claim 10 wherein the width 5 References C'ted by the Apphcant of said foil is less than that of the two strips to which it UNITED STATES PATENTS 15 connected 2,938,175 5/1960 Sommers.

References Cited by the Examiner 2983884 5/1961 Rueger' FOREIGN PATENTS HERMAN KARL SAALBACH, Primary Examiner.

718,957 11/1954 Great Britain. L. ALLAHUT, Assistant Examiner. 

1. MEANS CONNECTING STRIP TRANSMISSION LINES COMPRISING TWO STACKED CIRCUIT BOARDS EACH CONTAINING A FLAT CONDUCTIVE STRIP INCLUDED BETWEEN A PAIR OF CONDUCTIVE GROUND PLATES AND SEPARATED FROM SAID PLATES BY SOLID DIELECTRIC MATERIAL, EACH OF SAID STRIPS HAVING AN END POSITIONED DIRECTLY OPPOSITE THE CORRESPONDING END OF THE OTHER STRIP, A CONDUCTIVE STRIP OF FOIL HAVING THICKNESS AND WIDTH DIMENSIONS APPROXIMATING THE CORRESPONDING DIMENSIONS OF THE FLAT CONDUCTIVE STRIPS IN SAID BOARDS, MEANS ELECTRICALLY AND MECHANICALLY SECURING SAID FOIL TO THE ENDS OF SAID STRIPS, AND DIELECTRIC MATERIAL INTERPOSED BETWEEN SAID FOIL AND THE GROUND PLATES OF SAID STACKED CIRCUIT BOARDS. 